A. Kumar, K. Gupta, P. K. Gupta, B. Rastogi, B. Agrawal, and P. Kalra, “Clinical Efficacy of Nalbuphine Versus Tramadol as Analgesic Adjuvant to Fentanyl During Major Abdominal Surgery Performed Under General Anesthesia- A Double Blind Randomized Study”, AAN, vol. 4, no. 1, pp. 76-80, May 2019.